Phonograph reproducer



24, 1936. A. c. KELLER 2,034,872

PHONOGRAPH HEPRODUCER Filed Oct. 20, 1934 2 Sheets-Sheet l INVEN TOP AQKELLER ATTORNEY March 24, 1936. A. c. KELLER ,3

PHONOGRAPH REPRODUCER I Filed Oct. 0, 1954 2 Sheets-Sheet 2 FIG. 4

FIG. 5 7 FIG. 6 FIG. 7

INVENTOR By A.C./(ELLR A TTO NEY Patented Mar. 24, 1936 UNITED STATES PATE T FFHE 2,034,872 PHONO GRAPH REPRODUCER Arthur 0. Keller, Mount Vernon, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a. corporation of New York Application October 20, 1934, Serial No. 749,155

'7 Claims.

pable of high quality reproduction from either hill-and-dale or lateralcut records without requiring any attention on the part of the operator as to which type of record is being used.

According to the invention, the generating elel") ment, preferably a very thin coil of the pancake type, is mounted vertically on the stylus holder with about one-half of the coil projecting into a short gap in the magnetic circuit of the device.

This assembly is supported by vertically spaced .3- cantilever springs, the upper spring being free to deflect either vertically or laterally and the lower spring intermediate the coil and the stylus being free both vertically and torsionally, but relatively rigid in a lateral sense. When the stylus is vi- 0 brated vertically both springs deflect vertically and the upper portion of the coil turns act as the generating element, but when lateral forces are applied to the stylus the lower spring is deflected torsionally and the lateral portion of the coil 25 turns in the gap become the generating element.

In an alternate construction, according to the invention, the magnetic structure is of the crosspole type and so arranged that substantially onehalf of each coil turn is active for either type of 3- reproduction.

Due to the compact design of the moving system the mechanical impedance of these reproducers may be kept very low so that good tracking is obtained at 'low stylus pressures. Moreover,

35 the pancake coil can be made very thin and the air-gap very short and leakage flux relatively low so that particularly when a cross-pole magnetic structure is used the advantages of low stylus pressure are obtained with very little, if any, sacrifice in efllciency as compared with reproducers of other types.

Fig. 1 of the drawings is a perspective view of a reproducer according to the invention;

Figs. 2 and 3 are front and side views respectively of the reproducer of Fig. 1;

coil to confine the flux to the active portions of 10 shown and pole-pieces I I and I2 which define a substantially triangular gap l3 for the coil I4. The coil is spirally wound on a central core member l5 and suitably impregnated to make it rigid I enough to hold its shape without external sup- '5 port. In this way, the coil can be made very thin so that the gap l3 may be very short and the flux density in the gap very high. The pole-pieces are preferably slotted opposite the core l5 of the the coil and the efliciency of the device may, of course, be further increased by shaping the pole faces l6 and I! to the contour of the coil so that the path of lowest reluctance is through the coil.

The pole-piece l 2 is preferably made by cutting 1 away a portion of the bottom piece l8 to form th necessary triangular pole face I7 and at the same time provide vibrating clearance for the coil supporting springs l9 and 20. The pole-pieces II and I2 are conveniently held in their proper relative positions by a brass or other non-magnetic spacing piece 2| and the coil supporting springs l9 and 20 are secured to the bottom piece l8 by a screw 22 and a spacing washer 23. The upper V spring l9 should be free to deflect both vertically 25 and laterally and in the construction shown it consists of a single strand of fine steel wire secured to the center of the core I 5 of the coil. The lower spring 20 should be free to deflect both vertically and torsionally but not laterally and. these requirements are met by a V-shaped spring of wire or of thin sheet material with the center portion stamped out as shown. This spring is-preferably connected to a lightweight tubular member 24 which connects the stylus 25 to the coil. 36

When the reproducer is used on hill-and-dale records the springs l 9 and 20 will both deflect vertically to permit the coils to vibrate vertically with the stylus and the top quarter 26 of the coil as defined by the dotted line 21 and the side 28 40 of the pole-pieces l I will be effective to generate currents representing the sounds recorded on the record. When the reproducer is used on lateral cut records the spring 20 being relatively stiff laterally will deflect torsionally to form a pivot so 5 that the upper spring I 9 will deflect laterally and the coil will vibrate laterally in the gap. In this case the top quarter of the coil is inefi'ective but the lateral quarter 29 will generate currents representing the sounds recorded on the lateral rec- 0rd. It is therefore apparent that this reproducer may be used indiscriminately on either type of record.

In the alternate construction of Figs. 4 to 7 a cross-pole magnetic structure is used to increase the proportion of active conductor in the coil. The magnet 3| has two pole-pieces 32 and 33 each of which has two active pole faces on opposite sides of the coil 34 so disposed that the flux traverses the two halves of the coil in opposite directions as indicated by the polarity markings S1, N1 and S2, N2 in Figs. 5 and 7. In order to keep the leakage flux low, the spacing between the north and south poles on the same side of the coil must be large as compared with the working gap in which the coil is disposed and for the purposes of illustration the spacings have been shown larger than required in actual practice since the working gaps cannot be clearly shown in their true proportion.

The moving system comprising the coil 34, the stylus 35 and the connecting tube 36 is supported by the springs 31 and 38 which are secured to the pole-piece 33 by the screw 39 and the spacer 4D in a manner similar to the construction already described. The pole-pieces 32 and 33 are held in position by the non-magnetic spacer 4| as shown inFig. 4 but this spacer is omitted in Figs. 5 to '7 in order to show the magnetic structure more clearly.

From the description already given of the structure of. Fig. 1 it will be clear that. the portion of the coil .between the pole-pieces S1 and N2 will be operative as in the structure of Fig. l to generate currents in accordance with either lateral or vertical stylus vibrations. When the coil is vibrated vertically the top quarter. 42 is active and at the same time the bottom quarter 43 of the coil is cutting the flux between the poles N1 and. S2 which is flowing in the direction opposite to the flux between S1 and N2 so that the currents are in aiding relationship in the coil turns. Similarly, when the coil is vibrating laterally so that the side quarter 44 is active, theother side 45 will also be active to generate currents in additive relationship to those generated in thequ'arter 44 since the fluxes at the two sides of the coil are in opposite directions. In this structure, therefore, substantially one-half of the coil is active when the reproducer is operating on either type of record and a correspondingly higher efiiciency can be obtained.

What is claimed is:

1. In a universal reproducer, a moving. system comprising a flat spirally wound coil, a stylus and a stylus arm connecting the stylus to the coil, a magnetic circuit including a gap, and spring supporting means for the system constraining the coil to vibrate inthe gap in one generating. mode for vertical vibrations of the stylus and in another generating mode for lateral vibrations of the stylus.

2. A universal reproducer comprising a magnetic circuit including a short air-gap, a stylus, a stylus arm, a flat spirally wound coil on the arm, and means for supporting the coil for both vertical and lateral vibrations in the air-gap comprising an upper spring free to deflect both vertically and laterally and a lower spring relatively rigid in a lateral sense, but free to deflect vertically for vertical vibrations of the stylus and torsionally to form a fulcrum for the arm when the stylus is vibrated laterally.

3. A moving system for phonograph reproducers comprising .a flat spirally wound coil, a stylus, a connecting member between the stylus and the coil, and vertically and torsionally resilient mounting means comprising an upper spring support secured to the center of the coil and a lower spring support secured to the member for holding the coil in operative relation to a magnetic circuit.

4. A moving system for reproducers comprising a fiat spirally wound coil, a stylus; a connecting member between-the stylus and the coil, an upper supporting spring secured to the center of the coil and a lower supporting springfree to deflect both vertically and torsionally, but not laterally secured to the member intermediate the coil and the stylus.

5. In a universal reproducer, a movingsystem comprising a flat coil, a stylus and aconnecting member between the stylus-and the coil, a crosspole magnetic structure defining a plurality. of gaps and a plurality of springs supporting the coil for lateral and vertical vibrations in=said gaps.

6. Ina phonograph reproducer, a magnetic'circuit including two pole-pieces defining'a gap, a spirally wound coil, a stylus for driving the coil and spacedsprings difiering in lateral stiffness supporting the'coil for vertical and lateral vibrations with substantially one-half of the-coil extending into the gap.

'7. In a phonograph reproducer, a spirally wound coil, astylus for driving the coil, means for supporting the coil for both vertical and lateral vibrations and means for producing magnetic fluxes parallel to the axis of thecoil. but in. opposite directions in diagonally opposite halves of the coil.

ARTHUR C. KELLER. 

